The biosynthesis of retinal cell membranes is being explored using new techniques of immunochemical subcellular fractionation. The approach uses purified antibodies against rod outer segment proteins. Antibody to frog opsin prepared in rabbits and to cattle opsin prepared in sheep are used as probes to study the vectoral transport of newly synthesized opsin from the Golgi apparatus to the rod outer segment. Membranes are labeled using radioactive amino acid precursors injected into the vitreous cavity of the frog eye. Subfractionation of the retina yields fragments intensively labeled at transient periods after the injection of the radioactive amino acids. The label appears predominantly in two proteins, opsin and a large molecular weight protein of molecular weight 290,000. These antibodies are being used as specific affinity probes for the purification of the membranes involved in their biosynthesis. Synthesis of the N-terminal peptide of opsin is being explored by the Merrifield solid state technique to prepare specific probes for unique regions of rhodopsin sequence to determine the orientation of rhodopsin during synthesis and transport.